The judge who presided at the trial of Amanda Knox and her former Italian boyfriend, Raffaele Sollecito, has reportedly said they may be guilty after all.

Speaking just two days after he and his fellow judges handed down a full acquittal on appeal, Judge Claudio Pratillo Hellmann, said the court's verdict "is the result of the truth that was created in the proceedings. But the real truth may be different. They may be responsible, but the evidence is not there."

The 69 year-old judge was speaking to the Corriere della Sera newspaper in the latest of several interviews he has given to media organisations since reading out the verdict on Monday night. On Wednesday, he had already begun to muddy the waters, telling another interviewer: "This will remain an unsolved truth. No one can say how things went."

Hellmann's remarks were all the more unexpected because he and the other judges could have reached a less clear-cut acquittal. Italian courts have ruling options in which the appellants are acquitted for lack of evidence – a verdict similar to "not proven" in Scottish law.

Monday night's decision was the climax of a dramatic and at times searingly acrimonious appeal that attracted global attention. It was reached by Judge Hellmann and a second professional judge sitting alongside six lay judges drawn by ballot from among the public.

The acquittal of Knox and Sollecito meant that the only person left in jail for the 2007 murder of the British student Meredith Kercher is Rudy Guede, an Ivory Coast-born drugs peddler. He admitted he was in the house on the night she died, but denied he killed her. Guede is serving a 16-year sentence after opting for a fast-track trial.

Hellmann said: "I cannot affirm that Rudy Guede is the only one who knows what happened that night." But he added: "He certainly knows and hasn't said. Perhaps the two [other] accused, Amanda Knox and Raffaele Sollecito, also know."

Commenting on protests outside the court in Perugia after the verdict was announced, the judge observed that many Italians had already decided on Knox's guilt. "I think it stems from [her] American nationality," he said.

Hellmann added that he was sorry to see the prosecutors had taken the outcome as a defeat. "If I had been in their place, with the elements they had, I would have done the same," he said.

The prosecutor who led the investigation, Giuliano Mignini, has indicated that he wants to contest the court's decision in Italy's highest appeals tribunal. But the court, in Rome, normally deals only with points of law and procedure.